Here is a more secure way to reset password without skip-grant-tables

Suppose you want root to have myn3wp@ssw0rd as the password

Step 01 : Create a script to execute when mysqld first start up

Create a file called /var/lib/mysql/init-file.sql with these two lines

GRANT ALL PRIVILEGES ON *.* to root@localhost
IDENTIFIED BY 'myn3wp@ssw0rd' WITH GRANT OPTION;

Step 02 : Run these three(3) lines in the OS

chown mysql:mysql /var/lib/mysql/init-file.sql
service mysql restart --init-file=/var/lib/mysql/init-file.sql
rm -f /var/lib/mysql/init-file.sql

Step 03 : THERE IS NO STEP 03. YOU ARE DONE !!!

Give it a Try !!!

CAVEAT

• I used to recommend two restarts of mysql that required editing my.cnf
• I learned a better approach from @ShlomiNoach
• This answer improves on it more by not editing my.cnf at all

UPDATE 2013-06-17 07:05 EDT

OK Since mysqld for Ubuntu does not like init-file on the command, you must edit the my.cnf. Please do these next two steps

STEP 01) Add these lines to my.cnf under the [mysqld] group header

[mysqld]
init-file=/var/lib/mysql/init-file.sql

STEP 02) Allow mysql to read files from /etc/mysql

sudo vim /etc/apparmor.d/usr.sbin.mysqld

Add the line:

/etc/mysql/*.sql r,

STEP 03) Restart MySQL

This should work for you. Give it a Try !!!

Well, if you have full access to the database host you don't need to delete and re-create the password file.

According to Using Operating System Authentication section in Database Administrator's Guide logging in as an OS user which is a member of dba group on *nix or ora_dba group on Windows and connecting to an Oracle Database instance using SQL*Plus with SYSDBA or SYSOPER privileges should do the trick.

$ ssh root@orcldbxe1
[root@orcldbxe1 ~]# su - oracle
[oracle@orcldbxe1 ~]$ groups
oinstall wheel dba
[oracle@orcldbxe1 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.2.0 Production on Fri Aug 22 08:22:35 2014

Copyright (c) 1982, 2011, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

SQL> select status from v$instance;

STATUS
------------
OPEN

SQL>

That's why it's called operating system authentication – you use operating system group. Simple and convenient, and no need to remember passwords. I always use it.

Once you're in, you can reset passwords and do other administrative tasks.

SQL> alter user spongebob identified by s3cr3t;